Immobility, prolonged periods of lying down such as following surgery, peripheral vascular disease and diabetes are all examples of the kinds of things that are associated with pressure sores or pressure ulcers in patients.
Patients who are lying down for prolonged periods are particularly prone to developing pressure ulcers on or around the calcaneus and lateral malleolus of the foot. Patients with diabetes are highly susceptible to developing diabetic foot ulcers caused by poor circulation and patients with peripheral vascular disease are susceptible to developing arterial ulcers.
In such patients, mechanical pressure, moisture, friction and shearing forces all predispose to the development of pressure ulcers (see for example, Harrison's Principles of Internal Medicine, 14th edition, Fauci et al (eds), 1998, McGraw Hill, at 43).
There are a wide variety of prosthesis which have been developed for treating and/or preventing pressure ulcers. However, many of these, such as U.S. Pat. No. 4,197,845, U.S. Pat. No. 5,449,339, U.S. Pat. No. 4,186,738 and U.S. Pat. No. 4,104,746 all make some contact with the sole of the patient's foot making it potentially difficult for the patient to walk whilst wearing the prosthesis.
In addition, each of the above mentioned prior art examples, as well U.S. Pat. No. 5,957,874, all have the effect, that when the patient is wearing them and is supine, the height of the patient's foot relative to that of their knee is greater, causing the patient's leg to hyperextend. This can be uncomfortable and is not overcome by the prior art mentioned above.